Self-contained, underwater breathing apparatus (SCUBA) equipment is used by professional divers, military personnel, and amateur enthusiasts the world over to survive and maneuver underwater for extended periods of time. Such systems often employ a portable source of pressurized air, such as one or more tanks, and associated regulators, lines, mouthpiece, mask, etc. to enable the diver to comfortably breathe air at depths of 100 feet underwater or more.
A problem often associated with open system SCUBA equipment is the exhaust air breathed out by the diver after each breath. This exhaust air normally exits the regulator assembly adjacent the diver's mouth as a large grouping of bubbles that float upward to the surface (hence, “open system” SCUBA). Depending upon the spatial orientation of the diver, the exhaust bubbles can pass directly adjacent the diver's ear, which can be unpleasantly loud and annoying to the diver and can detract from the serenity that the diver might have otherwise enjoyed in the underwater environment. Bubbles passing in front of the diver's mask can also obscure vision and may in some instances cause a safety risk.
Expansive underwater environments, such as that existing under the surface of an ocean, can often have an “ambient” noise level made up of broad-spectrum “white” noise. While this noise can come from a variety of sources such as surface phenomena (e.g., wind, rain) and undersea animal life, a significant proportion of this white noise can often be attributed to bubbles of gas suspended within the water.
Undersea bubbles can be generated in a variety of ways, such as from the natural aeration provided by waves and currents, gasses from animals and plants, and methane or other gasses emitted into the water from underlying strata. This high frequency white noise often represents a normal background level for undersea life, in much the same way that high frequency noise from overhead UV lights or HVAC conduits are not usually noticed by human workers in an office building.
Noise vibrations can be generated when bubbles are formed, when a group of smaller bubbles coalesce into a larger bubble, and when a larger bubble collapses into a group of smaller bubbles. Bubbles also emit noise vibrations when they reach the water surface and the entrapped gas escapes into the atmosphere. It has been found that different sizes of bubbles produce different frequencies when they collapse, and the collapse of different sizes of bubbles release different levels of energy into the surrounding water.
As an extreme case, the so-called Snapping Shrimp (Alpheus heterochaelis) can hunt prey by snapping a specialized claw shut to collapse a cavitation bubble and release large amounts of energy sufficient to stun or kill a small fish. The energy level is so great that sonoluminescence (light generation) and temperatures of around 5,000 degrees Kelvin are produced during the cavitation event.
It follows that, under normal circumstances, undersea wildlife are largely undisturbed by high-frequency, low energy noise conditions, but may become startled and skittish in the presence of lower-frequency, higher energy noise conditions. Unfortunately, when a human diver exhales through existing regulators, large, quickly forming bubbles are produced, and these bubbles release low-frequency energy of the type that tends to scare off wildlife when the diver approaches. By contrast, it has been observed that free divers and divers using closed-circuit rebreathers in which no bubbles are released can normally approach and get very close to wildlife.